This invention relates generally to a pressure regulator and more particularly to a bypass-type differential pressure regulator for maintaining a substantially constant pressure drop across the high and low pressure sides of a fluid pressure system having a high pressure bypass line. Such a regulator may, for example, be used to maintain a constant pressure drop across the inlet and outlet of a metering valve which forms part of the fluid pressure system.
A typical bypass-type differential pressure regulator comprises a piston-like valve member which is adapted to move back and forth in a valve housing having high and low pressure ports communicating with the high and low pressure sides of the system. The valve housing also includes a bypass port for bypassing pressure fluid from the high pressure side of the system to the bypass line. High pressure fluid admitted into the housing biases the valve member to a position tending to open the bypass port while a spring coacts with low pressure fluid admitted into the housing to bias the valve member to a position tending to close the bypass port. If the high pressure increases or the low pressure decreases, the valve member is shifted to bypass more flow from the high pressure side of the system to the bypass line and thereby maintain a substantially constant pressure drop across the high and low pressure sides of the system. Conversely, a decrease in the high pressure or an increase in the low pressure results in the valve member being shifted to bypass less flow and thus maintain the substantially constant pressure drop. A bypass-type differential pressure regulator of this general type is disclosed in Van De Mark U.S. Pat. No. 4,117,857.
Difficulty has been encountered with prior regulators in maintaining a constant pressure drop at various flows and particularly when there is a wide range of bypass flows. As the bypass flow increases and the valve member opens, the biasing force exerted by the spring becomes progressively higher and thus the valve member encounters progressively greater resistance against movement to an open position. Also, increasing fluid reaction forces resist opening of the valve member. As a result, the pressure drop across the system tends to increase at high bypass flow rates rather than remaining at a desired constant value.